EDITOR,—Considerable caution must be exercised in interpreting the results of Lyn March and colleagues' n of 1 trials in osteoarthritis.1 For example, the authors observe that “seven of he eight patients who changed treatment from baseline changed to paracetamol (P=0.07, exact binomial).” Of the 20 patients analysed, 16 were taking a non-steroidal anti-inflammatory drug and only three were taking paracetamol. Therefore, at most three patients could have changed their treatment from paracetamol.